Various operations require tools to be inserted into a well and fixed there temporarily. In some instances, packers are run into a wellbore and then set using slips and cones that fix the packer at a predetermined location to isolate an annular area of the bore. In other instances, bridge plugs or “frac” plugs are similarly installed to temporarily block the wellbore and provide a barrier against which pressure can be developed to treat a hydrocarbon-bearing formation adjacent the wellbore. In all of these instances, the tool is typically disconnected from a run-in string of tubulars and left in place during the operation. Thereafter, some of the tools can be retrieved to the surface while others must be destroyed with a milling device.
Increasingly, hydrocarbons are collected from wellbores that are not vertical but extend outward, sometimes horizontally from a central wellbore. These non-vertical wellbores are cased and completed just like their vertical counterparts and are also subject to the same treatments and tools. Tools can always be run into a non-vertical wellbore on rigid tubing but that requires a rig and complimentary equipment to connect the tubing as it is inserted and removed from the wellbore. Coil tubing is thin-walled, removable, continuous tubing without joints. Coil tubing is available for running tools into a well but must be transferred to the well site on large reels and then requires some type of injector to be installed in the wellbore.
Because of the above disadvantages of tubing, the preferred way to install many downhole tools is with wireline. Wireline is a cable comprising one or more conductors which provides real-time communication with a downhole tool and can also bear the weight of the tool. Wireline is designed to be reeled into a wellbore with the tool on one end. In operations requiring many tools to be placed in the wellbore, like fracturing operations including multiple zones, wireline installation saves time and money.
Problems with wireline installations arise with non-vertical wellbores simply because gravity is not available to help urge the tool down the wellbore. Rather than move along the center of the wellbore, the tools tend to rest on the low side of the bore, coming into contact with any debris that has settled there.
Various means have been used to overcome the problem of wireline delivered tools and non-vertical wellbores. In some instances the tools are “pumped down” with fluid pumped past the tool. This is partially effective but due to the position of the tool on the low side of the wellbore, a large annular gap extends between the top of the tool and the upper wall of the wellbore, making the pumping process partially ineffective. In other instances, tractors are used to help move a tool along a non-vertical portion of a wellbore. Tractors typically have at least one moving member that either rotates or oscillates against a wellbore wall. However, tractors are expensive, cannot be left in a well and add another layer of complication to a tool installation job.
There is a need therefore for a method and apparatus that can facilitate the installation of a tool into a wellbore, particularly a non-vertical portion of a wellbore. There is a further need for a tool that has a friction-reducing component to reduce the friction that necessarily arises as the tool moves along a non-vertical wellbore. There is a further need for a tool that has centering capabilities to reduce its tendency to sit on a low side of a non-vertical wellbore. There is yet a further need for a tool that can better utilize an annular area created between the tool and the wellbore to facilitate pumping down the tool with circulating fluids.